defn-spec

A Clojure(Script) wrapper around defn that optionally adds checking to a function's args and/or return value via assertions.

NOTE: This is an experimental idea. Feedback (good idea, bad idea, this/that doesn't work, etc.) is appreciated.

Installation

[defn-spec "0.1.0"]

Usage

You use defn-spec in the same way you would use defn.

(require '[clojure.spec.alpha :as s])
(require '[defn-spec.core :as ds])

(ds/defn-spec my-inc
  [x]
  (inc x))

Now let's add Spec assertions to the above function definition by adding an attribute map.

(ds/defn-spec my-inc
  {::s/args (s/cat :x int?)
   ::s/ret  nat-int?}
  [x]
  (inc x))

Open a REPL and try calling your new function...

(my-inc 1)
=> 2

(my-inc "a")
ExceptionInfo Call to user/my-inc did not conform to spec:
In: [0] val: "a" fails at: [:x] predicate: int?
  
(my-inc -2)
ExceptionInfo Return value from user/my-inc did not conform to spec:
val: -1 fails predicate: nat-int?

If defn-spec is not working, ensure s/*compile-asserts* is true.

In Production

Set s/*compile-asserts* to false for all defn-spec expansions to compile to a regular defn form.

(binding [s/*compile-asserts* false]
  (macroexpand-1 '(ds/defn-spec my-inc
                    {::s/args (s/cat :x int?)
                     ::s/ret  nat-int?}
                    [x]
                    (inc x))))
=> (clojure.core/defn my-inc 
     #:clojure.spec.alpha{:args (s/cat :x int?), :ret nat-int?} 
     [x] 
     (inc x))

License

Copyright © 2018 Provisdom

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.